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Sept. 7, 2010 -- Infants and young children who don’t get enough sleep at night may be more likely to become obese before adulthood, a new study says.

And napping doesn’t seem to be the answer for children who get insufficient nighttime sleep, researchers say. The study appears in the September issue of Archives of Pediatrics and Adolescent Medicine.

Obesity has doubled among children aged 2 to 5 in the past three decades, and it has tripled among youths between 6 and 11, researchers say. Obesity has also doubled in young people between 12 and 19.

Not Enough Sleep May Mean Obesity for Youngsters

Janice F. Bell, PhD, MPH, of the University of Washington, and colleagues, studied 1,930 children up to age 13, collecting data first in 1997 and then in 2002.

For purposes of the study, the children were separated into a group of zero to 4 years old and an older group of 5 to 13 years old.

At the follow-up check, 33% of the younger children and 36% of the older ones were overweight or obese, as determined by body mass index, or BMI, a commonly used ratio of a person’s height and weight.

For the younger children, short nighttime sleep was associated with increased risk of becoming overweight or obese.

In the older group, sleep duration in the beginning year of the study was not associated with subsequent weight status, the authors say.

But contemporaneous sleep was associated with increased odds of a shift from normal weight to overweight or from overweight to obesity at the follow-up year.

In addition, daytime sleep had little effect on the odds of becoming overweight or obese.

An Age ‘Window’ for Weight Gain

“These findings suggest that there is a critical window prior to age 5 years when nighttime sleep may be important for subsequent obesity status,” the authors write.

They note that sleep duration is a “modifiable risk factor with potentially important implications” for preventing obesity and treating it when it occurs.

“Insufficient nighttime sleep among infants and preschool-aged children appears to be a lasting risk factor for subsequent obesity, while contemporaneous sleep appears to be important to weight status in adolescents,” the authors write. “Napping had no effects on the development of obesity and is not a substitute for sufficient nighttime sleep.”

Unknown Biological Mechanisms at Work

The authors write that the biological mechanisms that influence a balance between energy intake and use are not known.

It may be that lack of nighttime sleep affects brain regions that regulate tiredness and metabolism, the researchers write.